With LTE Rel 8, a transmission band of 20 MHz was defined. In LTE-Advanced carrier aggregation will be used to support system bandwidths up to 100 MHz. This involves splitting the system bandwidth into five 20 MHz sub-bands, each centred on a respective component carrier. In order to be backwards compatible with LTE Rel 8 User Equipment (UEs), at least one of those sub-bands has to be LTE Rel 8 compliant.
It has been proposed for LTE-Advanced that, during handover, the target eNB (that is the base station of the cell to which the UE is moving), will tell the UE (via the source eNB, that is the base station of the cell in which the UE is currently located) which Component Carriers (CCs) the UE will be assigned to in the target cell. Thus, it has been proposed that at intra-LTE handover multiple Carrier Components (CCs) will be configured in the handover command for usage after the handover. This is to avoid the need for signalling this information to the UE after it arrives in the target cell so that the target cNB does not have to configure additional Component Carriers to the UE after the handover.